Peel, wash and halve the potatoes and cook in boiling salted water for about 20 minutes. Peel and chop the onions. Drain cucumber and beetroot separately, collect liquid. Cut both into fine cubes.
Cut the pickled herring in half. Heat 2 tablespoons of fat, fry onions lightly while turning. Roughly dice the corned beef, add to the onions and fry for approx. 2 minutes. Season well with salt, pepper and piement.
Drain the potatoes and mash them into puree. Add corned beef, 4-6 tablespoons beetroot juice and 2-4 tablespoons cucumber water and stir in. In the meantime heat 1 tablespoon of fat in a large pan and fry 4 fried eggs.
Season with salt. Arrange cucumbers, beetroot, rollmop, lobscouse and one fried egg each on plates.